Fuel control mechanism



Dec. 13, 1960 s. G. BEST 2,963,860

' FUEL CONTROL MECHANISM Filed July '7, 1958 3 Sheets-Sheet 1 IUT-76 @iDec. 13, 1960 s. G. BEST 2,963,860

FUEL CONTROL MECHANISM ATTORNEY Dec. 13', 1960 s.v G. BEs'r 2,963,860

FUEL CONTROL MECHANISM Filed July 7, 195s s sheets-sheet s F/G. 8 4f F/G 9 .z/z/fwJ i f7 z/ ATTORNEY 2363,36@ Patented Dec. 13, 1950 FUELCONTRL MECHANSM Stanley G. Best, Manchester, Conn., assigner to UnitedAircraft Corporation, East Hartford, Conn., a corporation of DelawareFiled July 7, 1953, Ser. No. 746,972

20 Claims. (Cl. G50-39.23)

This invention relates to turbine fuel control mechanism and inparticular to mechanism for controlling fuel principally in accordancewith speed at low powers and principally in accordance with temperatureat high powers and in accordance with temperature during changes fromone power setting to the other.

An object of the invention is mechanism which will give good turbinefuel control at low powers where temperature is generally constant overa large speed Irange and give good fuel control at high powers wheretemperature is critical and follows fuel ilow closely and is subject tocomparatively large changes with speed and to also give goodacceleration control with limits on the maximum temperature duringacceleration and limits on the minimum temperature during deceleration.

A further object is mechanism which will control fuel to accelerate theturbine from one speed to another and maintain a maximum permissiblesafe temperature during acceleration and quickly return the temperatureto a selected temperature when the iinal speed is approached.

A further object is a fuel control mechanism in which the engine actualtemperature signal is compared with a manually-selected,speed-responsive temperature signal, and an error signal is derived forcontrolling the fuel ow at the selected temperature.

A still further object is fuel control mechanism which will maintainacceleration at a maximum permissible temperature and deceleration at aminimum permissible temperature and return the control to a manuallyselected temperature upon completion of the acceleration ordeceleration.

Other objects and advantages will be apparent from the followingspecification and the attached drawings in which:

Fig. 1 is a schematic layout of a fuel control incorporating theinvention.

Fig. 2 is a detail showing the wiring arrangement of the limitingmechanism.

Fig. 3 is a set of curves showing operation of the fuel control.

Fig. 4 is a diagram showing the output of an A.C. generator and filtercircuits which can be used instead of manually actuated potentiometersto provide a speedvariable opposing voltage.

Fig. 5 is a curve showing the output of lter circuit of Fig. 4.

Fig. 6 is a diagram similar to Fig. 4 showing a ilter circuit producinga different output.

Fig. 7 is a curve showing the output of the filter circuit of Fig. 6.

Fig. 8 is a schematic diagram showing the fuel control of Fig. l appliedto a turbine driving an adjustable pitch propeller having a speedgovernor control.

Fig. 9 is a schematic diagram showing the fuel control of Fig. l appliedto a turbine having speed and thrust modifying exhaust nozzle regulatingeyelids.

Fig. 10 is a schematic diagram showing the control of Fig. l utilized tocontrol an adjustable pitch propeller with the fuel controlled by othermeans such as a manually actuated valve.

Fig. ll is a schematic diagram showing the control of Fig. 1 applied tocontrol the exhaust nozzle regulating eyelids with the fuel controlledby other means such as a manually actuated valve.

In the control of some jet engines, it has been found desirable to usethe engine temperature as a means for measuring fuel flow when thepilots lever is fully advanced -regardless of flight conditions. Thistemperature may be either turbine inlet or turbine dischargetemperature. Primary temperature control presents two problems. One isat low powers where the temperature might be constant over a wide rangeof speeds or even rise with decreasing speeds so that large speedvariations or statically unstable operation migh occur if temperaturealone were used as the means for regulating the fuel iiow. The otherproblem is that it is desired to operate the engine above the settemperature during periods of acceleration incident to advancing thepilots lever. This higher temperature is preferably the maximumpermissible safe temperature. When the engine has accelerated to itsfinal speed, it is desired to reduce the temerature quickly back to theselected value. The problem is to determine when the engine speed hasreached the desired final value at whichv the selected temperatureshould take control. The present invention provides a satisfactory meansfor solving both of the problems.

ln general, temperature is controlled by comparing an actual temperaturesignal from the engine with a manually selected temperature, or datum,signal and utilizing the difference, or error signal, to control fuelilow to change the engine temperature and eliminate the error signal.The selected, or datum, signal is produced by combining a selectedportion of a fixed electrical signal and a selected portion of a speedvariable electrical signal to give a datum signal which is to becompared with the actual temperature signal. The proportions of fixedand speed variable signals are varied with pilots lever position so thatat low powers the speed signal will predominate and hence, the enginetemperature will be compared primarily with a speed signal and theengine controlled in accordance with speed; that is, at low powers aspeed signal is used as a datum signal with which to compare the actualengine temperature signal. Means are provided for limiting the maximumdatum signal and also the minimum datum signal so that at low powers thedatum signals would follow a curve such as shown by the lines 10, 12 and14 of Fig. 3 as the turbine changes speed. The engine operatingtemperature is indicated by the curve 16 so that with the datum signalvarying rapidly in accordance with speed, the engine will settle out atan operating condition indicated by the intersection 18 of the lines 12and 16.

At the high settings, the proportion of the speed signal utilized isgreatly reduced and may even be eliminated so that the datum setting maybe a fixed temperature value similar to that indicated by the line 20 ofFig. 3, or it could have a temperature variation with speed as indicatedby line 26, smaller than the variation indicated by line l2 `and theengine would settle out yat an operating condition indicated by theintersection 22 of the lines 16 and 26. When the pilots lever is shiftedfrom a position indicated by the line 12 to a position indicated by theline 20, `an increase of fuel llow is called for which will increaseturbine operating temperature and the signal limiting rectifier thencomes into play to limit the temperature in accordance with the line 24so that the engine temperature will be limited to the maximumpermissible while accelerating, but the temperature will be reduced ormaintained at a constant selected value as the engine operatingcondition approaches the point 22. In a similar manner when the enginepower is reduced by bringing the pilots lever back to its low position,the minimum signal or temperature indicated by the line 14 will act as adatum and prevent -acomplete closing of the throttle valve and aconsequent flame blowout and will maintaintthe engine temperature'inaccordance withdine 14'. ,A

j As the engine speed approaches the speedin'dicated by the line 12 froma higherY speed, the datum" signal which will then be influenced largelyby speed will become large enough so as to'in'crease' the fuel flow tob'ring the temper ature up from that indicated byline 14 to an operatingcondition indicated bythe intersection 18`.

From the above, it will be noted that'y steady state operation isestablished at the intersection of the selected, or datum, temperaturecurve with` the curve of engine operating temperature. If the datumcurve has' a steep droop, such as Vindicated by the' line 12, theintersection will occur as substantially constant speed regardless ofshifts in the engineU operating curve; Ifthe droop curve isshallow', aslindicated by line 20v or Vdotted line 26, the intersectionwill be atsubstantially constantv temperature. The optimu'mslopeV may be somewherein between, with a1 consequent reduction in the amountV of turbine speedchange from the low setting to the high'nsetting where, it is felt, thatthe resulting lower speed at the high temperature" and power ispermissible. Stable operation is obtained at lowy speedy as long as the'droop of the line 12 is steeper than theV downward slope of engineoperating temperature'versus'speed as indicated by the line 16. Duringany acceleration' induced by power lever movement from the low to afhigh pilots lever setting, the turbine temperature immediately rises tothe maximum permissible value and remains there untilV the speed hasapproached closer to the tinal valuel then settles back smoothly to thefinal operating point. During a deceleration, the reverse action takesplace, the turbine temperature dropping to the minimum limit;

In genenal`the maximum temperature limit indicated by thevline 241would' notV be av constant or linear value, but wouldbeappropriatelyvaried with'speed and compressor inlet' air temperature asrequired to prevent surging of the engineV compressor. The minimum limitwould also be varied with speed'and'inlet'temperaturelto prevent leanblowout ondeceleration.

Mechanism' for accomplishing. theI aboveV results is schematicallyshown' in' Figi l in` which-via" turbine-compressor 28with^ thecompressor inlet on the left-hand end and the turbine exhaust on theright-hand endY of the engineas viewed infPig. l iss'hownasidrivingiagenerator 30, and-having compressore inlettemperature responsivedevices-'32,;fuel jets'f3'4I and`i'gn'iter'36 and turbine temperatureVsensing mechanism 381 Fuel is supplied to the jets or nozzle 34 by apump *40'taking fuel through an inlet 42 fromfa supply not shown :anddelivering'the fuel through: a pipe 44 to ay tlu'ottl'evalvef46.`controlling the ow through aline 4'8" to the nozzles-34; A valve 50responsive to the pressureon opposite sides'of` the throttle valve 46controls a by-'pa'ss around the pump 4t) to maintain constanttthepressure drop across the throttle valve 46.` Throttle valve 46 ispositioned by a bellows 54 and a valve 52which controls the pressure inbellows 54l A spring, noty shown, but preferably located inside thebellows normally closes the valve 46; Valve'SZ connects the interiorofthe bellows 54through lines -56 and 57 with a pressure which is the'same as the pressure outside of the bellows to permitV the spring (notshown) to move the bellows toward a closed position* and connects theinterior of'th'e bellows through lines57 andY 58 with a pressure lessthan the pressure outside'of thebellows to overcome theetfect'sfofjthespring and 'openthe valvfe'46. The'position vrof'valv'e 52 is`controlled by a proportional solenoid 60"s'in1ilar to that shown anddescribed in Best Patent 2,579,723; The proportional solenoidis'ractuated by an error' signal brought in on line`981fron1 the sensingmechanism-about to be'described;

Generator 30 which is driven at a xed ratio of the turbine-compressorspeed may be a D.C. generator whose voltage output varies with speed,but is preferably an A C. generator whose voltage varies with speed andwhose output is rectified to give a D.C. signal. Generator 30 isconnected through lines 62 and 64 and a rectier 66 with a potentiometer68. The convention used in connection with the rectiers is that thecurrent, as opposed to electrons, flows in the direction of the arrow sothat as shown, the potentiometer 68 would be plus on the lefthand sideand negative or Zero on the ground side.

The wiper 70 of the potentiometer 68 is connected through line 72 withthe positive side of the potentiometer 74 connected across a Xed sourceof voltage 76. Potentiometer 74 is provided with a wiper 78 which isconnected by rod with the Wiper 70 of potentiometer 68 and with -apilots lever 82 so ythat wipers 70 and 78 may be simultaneously actuatedby movement of the pilots lever. Wiper 78y is` connected throughresistance's 84, 86 and SS'to a junction 90 which is also connectedthrough resistance 92 and a reference junction; compensator 94 withtemperature' sensing or tail pipe thermocouples' 38. 'Ihe signalproduced at junction 90 Yi's A the error signal which is passed throughav D C. ampliiierV 96 and then through line 98 tothe proportionalsolenoidy 60' for controlling the fuel ow.

The tail pipe thermocouples 38' generate a positive D.C. voltage signalproportional to engine operating temperature, which signal after passingthrough resistor 92 is mixed with'the temperature setting signal comingthrough resistor 8S toproduce the error signal energizing proportionalsolenoid 60.

The positive side of the constant reference voltage 76 and potentiometer74 are connected to ground through wiper 70 and potentiometer 68. Hence,the output of the potentiometer 74 through its wiper 78"Will be anegative voltage with respect to arm 70; The circuit is arranged so thata` negative voltage will call for more fuel and a higher temperature.That is, an increase in the negative voltage applied to resistor 88 willrequire a higher tail pipe temperature which willl givea` more positivevoltage in resistor 92 in order to balance the increased negativevoltage in 88 and produce a null signal at junction 9i) which willde-energize solenoidy 60, returning valve 52 to a neutral position' andlhold' valve 54 in a xed position calling for no fuel change. 'I'heoutput of thev wiper 70 is al positive voltagewith respect to groundwhich is proportional to the engine Speed. The positive voltage `fromwiper 70 is'addedv in` series, in a bucking relation, to the output ofthe potentiometer 74 to give a temperature setting output of the wiper78 which varies with respect to ground` in af desired manner with speed.At high power settings` of the pilots lever 82, a small portion ofgenerator voltage is selected so that speed has ya minor elfect `and thevoltage output of the poteutiometersV is a negative voltage determinedlargely by the xed voltage source 76, thus giving a shallow'droopcharacteristic to the line as' indicated by line 26 of Fig. 3. At lowpower settings oftheY pilots lever 82, a large portion of the generatorvoltage of the potentiometer 68 is selected so that the speed-doesmostof the controlling, thus giving the steep` droop to the temperaturesetting signal as indicated by line 12 of Fig. 3.

Thecondenser 100`is inserted between resistors 86`and 88 and connectedwith groundk to'introducea lag in the setting signal, during changesproduced by changing the pilots lever A82'whose time constant would thenbe approximately equal to the time constantl of the thermocouple 3S inorder that the actual temperaturerather than the indicated temperaturewill -accunately follow the settingvoltage appearing at junction 102.

Maximum and minimum limit scheduling circuits 1414 and are provided forliniiting'thev maximum temperature schedulingV s ignalf and the minimumtemperature schedulingsignal to limit the maximum and' minimum operatingtemperature of the engine. The maximum limiting circuit 104 is designedto provide an output voltage equal to the desired maximum limitingtemperature setting voltage at point 102 and is varied in an appropriatemanner with speed and ambient temperature to prevent surging. The outputimpedance of the circuit 104 must be low with respect to resistor 84. Arectier 106 connects resistor 84 with the maximum lnniting circuit 104.So long as the voltage at junction 102 represents a temperature settingbelow maximum, it will be positive with respect to the negative outputof the limit scheduling circuit 104, and the rectier 106 will benonconducting so the circuit 104 will have no eiect on the junction 102.However, if the voltage in ywiper 78 entering resistor 84 is such as toattempt to produce a voltage at 102 more negative than established bylimiter 104, the rectier 106 will conduct, preventing the voltage at 102from appreciably exceeding that set by the limit scheduling circuit 104.

The limiting circuit 104 is shown in more detail in Fig 2 in which theexterior connections are arranged in a manner similar to that shown inFig. 1. The A.C. generator signal is brought in on line 108; constantnegative voltage from a voltage regulator tube (not shown) is brought inon line 110; the connection to the rectier 106 is brought in on line112; and the connections to the ambient temperature sensing mechanism 32are brought in on lines 114. The voltage from the A.C. generator is putthrough a grounded bridge comprising resistors 116 and 11S on one sideof the bridge and resistor 120 and condenser 122 on the other side ofthe bridge. The two sides of the bridge are connected by rectifier 124,resistors 126 and 128 and a second rectier 130. The negative constantvoltage source 110 is connected through a voltage divider 132 and 134 toground. An intermediate point 136 of the voltage divider 132, 134 isconnected through a rectier 138 with the midpoint 140 of the bridgecross connection and the constant voltage source is also con nectedthrough a resistor 142 to the point 144 between resistor 128 and rectier130 on the bridge cross connection. Filtering condensers 146 areprovided for the bridge cross connection.

In this limiter circuit so far described, the generator voltage whichincreases with speed is rectied to provide a positive voltage which isintroduced to resistor 126. The generator voltage is passed through thecircuit 120, 122 which will give it a faster rising characteristic thanthat introduced to rectifier 124, and is introduced to rectier 130tending to produce a negative voltage at junction 144 which will risefaster with increases in frequency of the generator voltage than theVoltage introduced to resistor 126. However, the constant negativevoltage from the constant voltage source 110 introduced to junction 144initially is greater than the generator output introduced to rectifier130 so that the rectier will not conduct. Hence the voltage at junction140 will be the negative voltage from the source 110 after passingthrough resistors 142, 123 reduced by the positive voltage comingthrough resistor 126 so that initially the numerical value of thenegative voltage at junction 140 will decline with increasing speed toprovide the downwardly sloping portion of limiting curve 24 of Fig. 3 atthe lower speeds by reducing the negative bias in line 112 leading tolimiting rectier 106. As the speed increases, however, the generatorvoltage introduced to rectier 130 will become greater than the constantvoltage at 144 so that rectifier 130 will conduct and thus tend toincrease the negative voltage at junction 144. This negative voltage,increasing faster with increases in speed than the positive voltageintroduced to resistor 126 because of the better conduction oi condenser122 at higher frequencies, will increase the negative voltage atjunction 140 with increases in speed and thus produce the rising portionof the curve 24 of Fig. 3 at the higher speeds. When the voltage at 140reaches or exceeds the voltage at junction 136 in the constant voltagedivider, rectifier 13S will conduct and thus limit the negative voltageobtainable and produce the line 20 of Fig. 3 which is substantiallyconstant with changes in speed. The resultant negative voltage atjunction is led through a rectier 148 and resistors 150, 152, 154 toground. Resistors 150, 152 and 154 form a voltage divider from which thenegative voltage from junction 140 applied to the backside of rectier106 is obtained. The voltage from the temperature sensing resistor 32 isfed into the junction 156 between lresistors and 152 to raise or lowerthe limits in accordance with ambient temperature by adding orsubtracting from the Voltage being fed from the junction 140. It willthus be apparent that the limiter 104 provides a voltage on one side ofrectiiier 106 at `all times which will determine by conduction ofrectiiier 106 when the negative voltage at 102 exceeds the negativevoltage in line 112 the maximum limiting temperature setting negativevoltage at point 102 and which is varied in the appropriate manner withspeed and temperature.

The minimum limiting circuit is substantially the same as the limitingcircuit 104, eXcept that it provides a smaller voltage and the rectier158 is of reversed polarity which, with respect to rectifier 106, willconduct when the voltage introduced to resistor 142 attempts to operatepoint 102 at too low a temperature setting. This low temperature settingwould, of course, be a voltage at 102. When rectifier 158 conducts, itwill prevent Ithe negative Voltage at 102 from dropping to a numericalvalue below the limit set by the limit scheduling circuit 160.

The resulting negative voltage at 102 is the temperature setting. It ispassed through resistors 36 and 80 and mixed with the positive terrnocouple voltage passing through resistor 92. Zero error voltageresults at the junction 90 when the turbine temperature is at the setvalue. A positive error voltage results if the turbine temperature istoo high and a negative voltage if it is too low.

Condenser 100 introduces a lag in the setting whose time constant shouldbe approximately equal to the thermocouple time constant in order thatthe actual turbine temperature, rather than that indicated by thethermocouple, will accurately follow the setting voltage at 102. For asteep increase in lever position, an overshoot of actual turbinetemperature would otherwise occur if the indicated temperatureintroduced to junction 90 followed accurately the voltage at junction102.

The error voltage at junction 90 is amplied in the D C. amplifier 96 andapplied through a line 98 to the proportional solenoid 60 in the fuelmetering hydraulic system. Integral feedback in a degenerative sense isused around the amplier to provide damping and to permit the use ofhigher sensitivity than would otherwise be possible.

While the potentiometer 68, selecting the desired proportion of thespeed responsive voltage has been described as a preferred means otmodifying the slope of curves 12 and 26 of Fig. 3, thus varying theslope of the droop with the speed, this droop change may be produced byother means. For instance, an alternator can be used with a lter circuitsuch that the A.C. output voltage of the tilter varies with speed asshown by Figs. 5 and 7. Either type of curve can be used. In eithercase, the slope is steeper at moderate speed than at high speed. Theoutput of the lter would be rectified to a positive D.C. voltage in thecase of the curve of Fig. 5, or a negative voltage in the case of thecurve of Fig. 7 which would be added directly to the voltage of thetemperature setting potentiometer 74 and would be used in place of thedroop slope adjusting potentiometer 63. The iixed voltage Vfor the datumsignal would be selected by the potentiometer 74, 78 and the value ofspeed voltage available to be combined with the xed signal would accessothese curves. Fig. 4 shows a simple example for producing the curve ofFig. 5 in which an alternator 162 has' a load circuit of a resistor 164and a kcondenser 166 and the output is taken across the condenserCircuit. The filter circuit shown Vin Fig. 6 could be `used forproducing the curve of Fig. 7. This iilte'r circuit comprises analternator 168v with a series of resistors 170, 172, 174 in one side ofthe generator output with condensers 182, 184 and 18'6 connecting theseveral pairs of resistors with the output taken across the lastcondenser 186.

While this invention has been disclosed for use with a jet engine, it isusable as a fuel control for either propeller turbine engines or forengines having variable area exhaust nozzles as shown in Figs. t?)y and9. In connection with Fig. 8, a turbine engine 28 drives a propeller 208and the turbine speed would be controlled by the propeller 208 by meansof the usual propeller speed governor 210 which would provide anvariable load for the turbine and thus control the speed. This speedcould be set by adjusting the usual governor Speeder spring by the samepilots lever 82 as used to set the temperature. In this case,Vequilibrium operation would be established by varying the fuel valve toobtain equilibrium at the exact speed at which the propeller control isset rather than at the intersection of an engine operating curve wth aspeed responsive temperature curve or a straight temperature curve.VThus the temperature signal would be selected by the potentiometers 68and 74 in the manner described above and this signal combined with theactual measured engine temperature signal to provide a fuel controlsignal which would change the temperature but would not change the speedwhich would 4be held constant by the propeller. There would be noinstability at low speeds because the speed would be substantially xedand the temperature would respond readily to any changes in fuel ilow.

For variable area exhaust nozzle engines shown in Fig. 9, the same typeof control would be used except the speed would be controlled by aturbine-speed responsive governor 212 controlling a variable areaexhaust nozzle, the area being varied in the usual manner by a motor 214actuating eyelids 216.

For both of these latter applications and even for the xed area jetapplication on which the present detailed specification is based, it maybe considered desirable to provide overspeed protection in the controli.e. provide protection against speeds above the normal speed range ofthe turbine. This can be' done by arranging the maximum limitingscheduling circuit so that it cuts back with a rather steep slope,similar to that indicated by the dotted line 26 in Fig. 3, withincreasing speed above a certain selected high speed',y thus reducingthe temperature setting to a low value. This may bedone by connectingthe output of the generator 30 through'line 200, Fig. 2, with arectiiier 202, a resistor 206, and a second rectiiier 207 with thejunction 156 so as to add a positive voltage to reduce the negativevoltage at the junction 156' and thus reduce the negative voltage inline 112 back of the rectiiier 106. This will permit 105 to conduct andlreduce the negative voltage at junction 102 and thus permit the positivevoltage introduced to junction 913 from the thermocouple 38 topredominate and reduce the fuel flow and the engine speed. A condenser299 may be inserted between the rectier 202 and the resistor 206 to takeout any ripple that may be left in the rectiiied voltage. A resistor 211connects the negative constant voltage in line 110 with the junction 213between the resistor 205 and the rectifier 207. Thus the lixed negativevoltage in line l1!) is compared with the positive rectified output ofthe generator 30 and will prevent the application of any positivebiasing voltage from the generator 30 to the junction 156 until afterthe generator has attained a predetermined voltage indicatingoverspeed.-

The same general control schemeY can also be used as shown in Figs; l0and ll, utilizing the propeller `208v or the variable areanozzlekmechanisms 214, 216, to control the exact temperature instead ofthe speed in which case. the propellerpitch' or the nozzle area' wouldbe varied in accordance with a selected temperature. Mechanism such assolenoid 60 and valve 52 controlled by mechanism described in detailabove and shown schematically vat 218, could be used to control flowthrough pipe 2.251 leading to' servo mechanismv controlling thepropeller pitch or the nozzle area. VAlthough the servo mechanism hasbeen shown as single acting, it Will be understood that double actingmechanism could be used equally well. The fuel Valve lo would beControlled manually or by other suitable means and the fuel would besupplied to fuel line 43 by the usual pump' 4i) or other pressuresource'. The speed would then be established at the value Where' thedroop curve of the fuel control passes through the temperature value setby the propeller .or the area control. Rather steep droop lines would beused for that type of application to hold the speed within reasonablyclose limits as opposed to the shallow droop lines at high speed withthe preferred embodiment described hereiii. This could be done byoperating with the potentiometer slider 70 hired or manually set to givenearly full generator voltage or the potentiometer 68 might beeliminated and the generator voltage applied directly to the lefthaiidend of potentiometer 74.

Although the preferred embodiments have been shown and described herein,it will be apparent that various changes and modifications may be madein the construction and arrangement ofthe various parts withoutdeparting lfrom the scope of this novel concept.

I claim:

1. A control for 'a gas turbine comprising a power lever, meanscontrolling turbine thrust, turbine temperature responsive means,turbine speed responsive means, means connecting said temperatureresponsive means and said speed responsive means with said thrustcontrolling means for controlling saidV thrust, and means actuated bysaid power lever selecting said temperature responsive means astheprincipalr thrust controlling variable yat high power settings of saidpower lever and said speed responsive means Ias the principal thrustcontrolling variable at low power settings.

2. A control as claimed in claim l including means actuated by saidpower lever gradually changing the relative proportions of temperatureand speed as controlling variables between low and high powers.

3. A fuel control for `a gas turbine comprising means producing lasignal responsive to turbine speed, means combining said speed signalwith a selected liXed signal to provide a combined signal, saidcombining means including means varying at least one of said signals tovary the proportion of the two signals in the combined signal andproduce a relatively large speed signal at low powers and a relativelysmall speed signal at high powers, means producing a signal responsiveto eng'ne temperature, means comparing said combined signal with saidtemperature signall and producing an error signal, means metering fuelto said turbine in proportion to said error signal, means between saidcombining means and said comparing means hunting the minimum availablevalue of said combined signals to limit the minimum turbine temperature.

4. In a fuel control for fa gas turbine engine,rvalve means controllingthe flow of fuel to the turbine engine, means producing a signal inaccordance with turbine operating temperature, means producing a datumsignal,

valve positioning means comprising means comparing saidV turbinetemperature signal with Vsaid datum signal,

and means responsive to any diderence inf said signals for actuatingsaid valve positioning means, means for adjusting said datum signal toprovide diierent turbine powers, said adjusting means including meansproducing a speed signal responsive to turbine speed as a portion ofsaid datum signal and means increasing the effectiveness of said speedsignal on said datum signal at low powers and decreasing theeffectiveness `of said speed signal on said datum signal at high powers.

5. A control as claimed in claim 4 in which said adjusting meansincludes means varying the ratio of turbine speed to speed signal.

6. A control as claimed in claim 4 in which said speed signal is anelectrical signal and said adjusting means includes a lter circuitvarying the ratio of turbine speed to speed signal.

7. ln `a fuel control for a gas turbine engine, valve means controllingthe flow of fuel to the turbine engine, means producing a signal inaccordance with turbine operating temperature, means producing anelectrical datum signal including a potentiometer connected across asource of fixed voltage and connected in series arrangement with thewiper of a second potentiometer which is connected with a source ofvoltage variable with speed, valve positioning means comprising meanscomparing said turbine temperature signal with said datum signa-l, andmeans responsive to any difference in said signals for actuating saidvalve positioning means, means for ladjusting said datum signal toprovide different turbine powers, said adjusting means including meansproducing a speed signal responsive to turbine speed as a portion ofsaid datum signal and means increasing the effectiveness of said speedsignal on said datum signal at low powers and decreasing theeffectiveness of said speed signal on said datum signal at high powers.

8. A fuel control for a gas turbine comprising means for selecting theturbine operating temperature, including means for selecting `a signalto be compared with an engine operating temperature signal to provide -atemperature error signal, means responsive to said error signalcontrolling the fuel ow to said turbine in proportion to said errorsignal, said selecting means including a xed signal, a signal Varyingwith turbine speed, means combining said signals land means manuallyvarying said fixed signal and simultaneously varying the proportion ofsaid speed varying signal to be combined with said iixed signal toprovide said selected signal.

9. A fuel control for a gas turbine comprising means producing a signairesponsive to turbine speed, means combining said speed signal with `aselected xed signal to provide a combined signal, means forsimultaneously manually decreasing one signal and increasing the othersignal to vary the proportion of the two signals in the combined signal,means producing a signal responsive to turbine temperature, meanscombining said combined signal with said turbine temperature signal toprovide an error signal, means metering fuel to said turbine inproportion to said error signal, means connected with said combinedsignal to limit the maximum value of said combined signal and meansconnected with said combined signal to limit the minimum value of saidcombined signal to thereby limit the maximum and minimum temperature.

l0. -A jet engine fuel valve control comprising means producing atemperature signal proportional to engine temperature, means producing aspeed signal proportional to engine speed, means selecting a portion ofsaid speed signal, means producing a steady signal, including meansselecting a desired portion of a fixed signal, means combining saidselected portion of said fixed signal with said selected portion of saidspeed signal to provide a datum signal, power control means actuatingboth said selecting means to vary said datum signal, means combiningsaid datum signal with said temperature signal to produce an errorsignal and means responsive to said error signal actuating said fuelvalve to Vary the -uel ow and change the engine temperature and speed toeliminate said error signal.

1l. A control as claimed in claim 10 in which the power control inmoving to a low power position selects a large portion of the speedsignal and a small portion of the fixed signal to combine to produce thedatum signal.

l2. A control as claimed in claim l() in which the power control inmoving to a high power position selects a small portion of the speedsignal and a large portion of the fixed signal to combine to produce thedatum signal.

13. In combination with an engine having fan engine operatingtemperature substantially constant over a material speed range at thelower engine powers and increasing with speed at the higher enginepowers, means pro-I ducing a temperature signal in accordance withengine operating temperature, fuel control means including meansestablishing a datum signal, means combining said engine temperaturesignal and said datum signal to produce an error signal and meansmodifying fuel ow by said error signal to change the engine temperatureand engine speed to eliminate said error signal, said datum signalestablishing means including, means selecting the desired engine power1and, at lower power positions including, means establishing a datumsignal equivalent to the maximum permissible engine temperature below aselected engine speed, and speed responsive means effective, within aselected minor engine speed range above said selected speed, to reducesaid datum signal to a signal equivalent to the minimum permissibleengine temperature and iat the higher power setting positions includingmeans establishing a signal equivalent to the maximum permissible enginetemperature up to a selected temperature and maintaining said datumsignal less subject to variations with speed to provide a signal morenearly equivalent to a selected temperature for a material change ofhigher speeds.

14. ln combination with an engine having an engine operating temperaturesubstantially constant over a material speed range at the lower enginepowers and increasing with speed at the higher engine powers, meansproducing a temperature signal in accordance with engine operatingtemperature, fuel control means including means establishing a datumsignal, means combining said engine temperature signal and said datumsignal to produce an error signal and means modifying -fuel iiow by saiderror signal to change the engine temperature and engine speed toeliminate said error signal, and means selecting the desired enginepower, said datum signal establishing means including means limiting thedatum signal at one extreme to a signal representing the maximumpermissible engine temperature, means limiting the datum signal at theother extreme to a signal representing the minimum permissible enginetemperature, speed responsive means controlled by said power selectingmeans effective at the lower end of the engine power range within aselected minor engine speed range to control said datum signal betweensaid maximum signal and said minimum signal and means controlled by saidpower selecting means effective at the upper end of the power rangereducing the effect of speed on said datum signal.

15. In combination with an engine having an engine operating temperaturesubstantially constant over a material speed range at the lower enginepowers and increasing with Speed at the higher engine powers, enginetemperature responsive means producing an electrical signal proportionalto engine temperature, means establishing an electrical datum signal,means combining said electrical signals to produce an electrical errorsignal proportional to the variation of said temperature signal fromsaid datum signal, and fuel control means modifying fuel flow by saiderror signal to change engine temperature and speed to eliminate saiderror signal, means selecting the desired engine power by modifying thedatum signal, said datum signal establishing means including a firstrectifier having a predetermined bias limiting the datum signal at oneextreme to a value representing the maximum permissible enginetemperature, means responsive to speed varying the basis of said rstrectiner to reduce the maximum temperature limit as speed increases fromzero speed up to a selected higher speed and otherrspeed responsivemeans varying said bias in the opposite direction above said selectedspeed to increase the maximum temperature limit `as the turbine speedincreases above said selected speed, and a second 'ectiiier limiting thedatum signal at the other extreme to a value representing the minimumpermissible engine temperature, means producing an electrical signalresponsive to speed, an electrical signal source or" fixed value, meanscombining said speed responsive and said iixed electrical signals toproduce said datum signal and means controlled by said power selectingmeans to select said speed responsive signal as the predominating signalat low power positions and said lixed signal as the predominating signalat high power positions.

16. A fuel control as claimed in claim 4 for a turbine driving acontrollable pitch propeller, and including a governor driven by saidturbine controlling the pitch of said popelle'r to maintain said turbinespeed at selected values, governor setting means for selecting saidvalues, and means connecting said governor setting means with said datumadjusting means.

17. A fuel control as claimed in claim 4 for a turbine having a variablearea `exhaust nozzle and including a governor driven by said turbinecontrolling said nozzle area to maintain said turbine speed at selectedvalues, governor setting means for selecting said values and meansconnecting said governor setting means with said datum adjusting means.l

18; A control for a gas turbine comprising means producing a signalresponsive to turbine speed, means combining said speed signal with aselected fixed signal to provide a combined signal, said combining meansincluding means varying at least one of said signals relative to theother to vary the proportion of the two signals in the combined signal,means producing a signal responsive to engine temperature, meanscomparing said combined signal with said temperature signal andproducing an error signal, means varying the thrust of said turbine,means responsive to said error signal controlling said thrust varyingmeans, means connected with said combining means between said combiningmeans and said comparing means limiting the value of said combinedsignals to limit turbine temperature. t,

19. A control as claimed in claim 18 in which said turbine has a normalspeed range and an overspeed range and including means responsive tospeed varying 12 the eect of said limiting means to vary the maximumtemperature over the normal speed range and other means responsive toianoverspeed of said turbine biasing said limiting means to reduce theavailable value of said combined signals. Y

20. In combination with an engine having an engine operating temperaturesubstantially constant over a material speed range at the lower enginepowers 1and increasing with speed at the higher engine powers, enginetemperature responsive means producing an electrical signal proportionalto engine temperature, means establishing an electrical datum signal,means combining said electrical signals to produce an electrical errorsignal proportional to the variation of said temperature signal fromsaid datum signal, and 'fuel control means modifying fuel ow by saiderror signal to change engine temperature and speed to eliminate saiderror signal, means selecting the desired engine power by modifying thedatum sigu'al, said datum signal establishing means including la irstrectifier having la 'predetermined bias limiting the datum signal at oneextreme to aV value representing the maximum permissible enginetemperature, and a second rectifier limiting the datum signal at theother extreme to a value representing the minimum permissible enginetemperature, means responsive to speed increase varying the bias of saidfirst rectifier to reduce the maximum temperature limit from zero speedup toa selected higher speed and increase the maximum temperature limitas the turbine speed increases above said selected speed, a thirdrectifier limiting the bias of said first rectifier to a predeterminedconstant value, means producing an electrical signal responsive tospeed, an electrical signal source of xed value, means combining saidspeed responsive and said lixed yelectrical signals to produce saiddatum signal and means controlled by said power selecting means toselect said speed responsive signal as the predominatingsignal at lowpower positions and 'said rst signal as the predominating signal at highpower positions.

References Cited in the le of this patent UNITED STATES PATENTS

